In a number of recent biology meetings, plant growth factors have been a favorite topic. One may ask if a new colloquium devoted to the metab olism and the activities of cytokinins, considered at the molecular level, was really necessary and will add anything important to the previous contributions. As a matter of fact, the primary purpose of the organizers, of the French National Center of Scientific Research, and of the National In stitute of Agronomic Research which sponsored the colloquium was less the edition of a proceedings book than the desire to bring together a number of scientists who had made contributions towards solving prob· lems in cytokinin research and thereby to provide an opportunity for fruitful discussions without restrictions in the timetable. Indeed this primary target was attained. Moreover, important new fmdings and con clusions were presented by the participants that merited publication in the form ofthis book. It is beyond the scope of this foreword to adver tize or even to classify these new fmdings. We shall only mention a few of them. The reader will appreciate the contributions of those authors who worked hard to elucidate the biosynthetic pathways of natural cytokin ins.

Inhalt
Section 1. Cytokinin Biosynthesis.- Analytic Procedures for Cytokinins: Application to Agrobacterium tumefaciens.- Cytokinin Biosynthesis and Its Relationship to the Presence of Plasmids in Strains of Corynebacterium fascians.- Cytokinin Biosynthesis in Higher Plants.- Biosynthesis and Enzymic Regulation of the Interconversion of Cytokinin.- Cytokinin Biosynthesis in Cytokinin-Autonomous and Bacteria-Transformed Tobacco Callus Tissues.- Cytokinin Biosynthesis and Metabolism in Vinca rosea Crown Gall Tissue.- Section 2. Cytokinin Metabolism and Physiological Responses in Plant or Bacterial Systems.- Cytokinin Translocation and Metabolism in Species of the Leguminoseae: Studies in Relation to Shoot and Nodule Development.- Uptake and Metabolism of Cytokinins in Tobacco Cells: Studies in Relation to the Expression of Their Biological Activities.- Genetic Regulation of Cytokinin Metabolism in Phaseolus Tissue Cultures.- Metabolism of the Cytokinins in Mosses.- Cytokinin Activities of N-Phenyl-N'-(4-Pyridyl) ureas.- Towards an Understanding of the Mechanism of Cytokinin Activity in Mercurialis annua L. Sex Differentiation.- Relative Activities of Cytokinins and Antagonists in Releasing Lateral Buds of Pisum from Apical Dominance Compared with Their Relative Activities in the Regulation of Growth of Tobacco Callus.- Section 3. Cytokinin Hormone Receptors: Methods and Results.- Photoaffinity Labeling Reagents to Detect Binding of Cytokinins: Chemical Limitations.- Uptake of [14C]-8-Azido-N6-Benzyladenine, a Radioactive Photosensitive Cytokinin, by the Cells of the Moss Funaria hygrometrica L..- Cytokinins and the Hormone Receptor Concept.- The Current Status of Cytokinin-Binding Moieties.- Section 4. Cytokinin in Protein Synthesis and RNA Metabolism.- Control of Growth byCytokinin: An Examination of Tubulin Synthesis During Cytokinin-Induced Growth in Cultured Cells of Paul's Scarlet Rose.- The Cytokinin Control of Protein Synthesis in Plants.- Cytokinin Action on Transcription and Translation in Plants.- Covalent Insertion of N6-Benzyladenine into rRNA Species of Tobacco Cells.- Section 5. Cytokinins and Chloroplast Development.- Plastids and the Origin of Cytokinin Autonomy in Tobacco Tissue Cultures.- Influence of Cytokinin on Plastid Biogenesis in Rye Leaves.- Light and Fusicoccin as Tools for Discriminating Among Responses of Cotyledons to Cytokinins.- Studies on the Action of Cytokinin and Light in RNA Synthesis of Pumpkin Cotyledons by Autoradiography.- Plastogenesis and Cytokinin Action. Cytokinin and Light Interactions in Plastid Enzyme Formation of Detached Cucurbita Cotyledons.- Cytokinin Action on RNA Synthesis in Chloroplasts.- Effect of Cytokinin on Plastid Differentiation in Tobacco Cell Suspensions.- Plastid Proteins of Cytoplasmic Origin as Molecular Markers of Cytokinin Activity.- Section 6. Animal Systems Responding to Cytokinin or Cytokinin Analogs.- 6-Benzylaminopurine as a Growth Factor for Drosophila melanogaster Cells Grown in Vitro.- Use of N6-Benzyladenosine as an Analog of Internal Methylation (N6-Methyladenosine) in Studies of Post-Transcriptional Regulation of RNA in Human Cells Infected by Herpes Simplex Virus.- Calcium-mediated Transduction of the Hormonal Message in 1-Methyladenine-induced Meiosis Reinitiation of Starfish Oocytes.